DESCRIPTION: Excessive activation of G protein-coupled receptors and their target G proteins contributes to cardiovascular diseases such as hypertension, congestive heart failure, and vascular restenosis. Furthermore, mutations leading to constitutively active or "runaway" receptors have been found which play a role in genetic diseases and are likely to contribute to complex polygenic disorders of the cardiovascular system. There are two ways to block excess G protein stimulation which are effective against both constitutively activated and ligand-activated receptors: 1) inverse agonists and 2) inhibition of the signal downstream of receptor such as at the receptor-G protein (or RG) interface. To date, the RG interface has not been fully exploited as a possible target of drug action though it has great potential. Knowledge of the structural basis of RG interactions would facilitate the development of practical inhibitors at this useful and potentially specific drug target. The diversity of G protein subunits provides a rich basis for specificity with numerous alpha (a), beta(b)and gamma (y) subunit subtypes. Understanding precisely where on the G protein surface the receptor binds will greatly facilitate the design of specific drugs targeting this site. Since the Gab or Gay interface includes structural determinants from both subunits, this would be an ideal location for designing uniquely specific drugs acting downstream of G protein coupled receptors. This project will use a multi-faceted approach to study the structure and function of the RG interface. The specific aims of the present project are to utilize a genetic strategy to identify all functional contacts between receptor and G protein, to produce an atomic level molecular model of the receptor-G protein complex, to utilize biochemical cross-linking and functional studies to define the receptor G protein interface with emphasis on the contributions of G band y subunits, and to examine the changes in a2 adrenergic receptor-Gafty contacts that occur in different receptor and G protein conformational states. This work should greatly improve our understanding of the structural and mechanistic basis of RG coupling and should facilitate the design of drugs that target particular G protein subunit combinations.